It seems you did an "in place upgrade" install, keeping a lot of stuff from Vista, instead of doing a clean install.
You could try to clean it up, for example if it kept some files in C:\Windows.old. You can delete a lot of what's in there and only keep any personal documents, pictures, etc.
If it was mine, I would first save any valuable files onto another disk or DVD and then do a clean install as described here: Clean Install with a Upgrade Windows 7 Version
Doing it that way, you will need to reinstall all your programs in the new OS, but you won't be wasting space with old files from Vista, which are difficult to find, or to know what can be safely deleted. Also a clean install is more reliable than an "in place upgrade" which is what I guess you have done.